BEIJING - Climate change and a growing population mean China, which is already losing farmland to deserts and urban sprawl, could face a food shortfall of 100 million metric tons by 2030, a top weather official said.

"Global warming may cause the grain harvest to fall by 5 to 10 percent ... by 2030," the official China Daily quoted Zheng Guoguang, head of the State Meteorological Administration as saying.

Around the same time the country's population is expected to reach a peak of 1.5 billion, up from the current 1.3 billion.

To feed the extra mouths with lower yields of grain, Beijing would need an extra 10 million hectares of arable land, or around 8 percent of that currently under cultivation, Zheng told a conference in Inner Mongolia.

But China already struggles to provide food for one fifth of the world's population with just 7 percent -- and shrinking -- of global farmland. It became a net importer of food in 2004.

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Zheng did not say how China could find extra cropland, as cities encroach on rural areas and deserts spread.

It has drawn a "red line" of 120 million hectares of arable land to be preserved for farming through 2010, a senior official said this summer, but it is already approaching that figure.

Arid northwestern Ningxia Autonomous Region plans to move more than 200,000 farmers from areas hit by severe drought, the South China Morning Post reported on Thursday.

Warmer weather will shorten the growing period of some crops, leaving their seeds without enough time to ripen, and even a 1 degree Celsius rise in temperatures will increase evaporation, making it harder to irrigate plants, Zheng said.

Crop-damaging insects will also find it easier to survive winters, and become active earlier in the spring, requiring pest control that could make farming more expensive, he added.